So two things: 1) With the exception of crucible rep, every faction can earn rep very easily from PvE. This was true even if you didn't turn in mats. 2) Given the weekly cap on marks, which you'll need for that light level 30 gear, assuming you were to just farm vanguard marks, and retain the crucible marks, you're talking about 100 rep per week by turning marks into mats into crucible rep. You also get 20 crucible marks you won't have to earn in the crucible. It's a bounty. Beyond that, that's a lot of dedicated farming for rep. If someone wants to grind their rep that way, I say let them